Electronic measuring and detecting apparatus



Aug. 8, 1950 M. MAY 2,513,045

ELECTRONIC MEASURING AND DETECTING APPARATUS A Filed Dec. 18, 1946 2 Sheets-Sheet 1 V'E-ae L.

4INVENTOR MADEL! E MAY ALI 1MM;

ATTORNEYS M. MAY

ELECTRONIC MEASURING AND DETECTING APPARATUS Filed Dec. 18, 1946 Aug.. s, 195o 2 Sheets-Sheet 2 FIG. 6

NVENTOR MADE E MAY .r 90420111 ATTORNEYS Patented ug. 8, 19550 ELECTRONIC MEASURING AND `DETECTING *APPARATUS l Madeline May, =Chieago, Ill., assigner, -by mesne assignments, to.. New York Motor Coach Advertising` Inc., .acorporation of New' York ApplicatiOnDecemberl 18, 1946,'.Seria1'Nm .716,979

' y 2 Claims. (C1. 175--183) This .inventionrelates kto measuring .and .detecting apparatus... and particularly tosuch devices utilizing .electronic means to detectand measure variations t in capacitance `between spaced electrodes inan oscillatorcircuit.

The main objects of this invention .are .to` provide an improved andmore sensitive measuring and detecting-.meansifor determining variations `from a predetermined standard in physical objects; Yto provide such a meansthat .is'operable with'both conductive andnon-conductive objects; to provide. such a means capable ofactuating visual indicating devices or mechanical sorting meansupon minute variations from Aa. predetermined normaly of v.the .dielectric `characteristics of. material under test; lto provide an improved detecting and measuring means whereby minute variations of the dielectric characteristics of material under test. produce rapid and relatively wide changes Ain visualiindicating means orelectro-mechanical apparatus; and to provide improved and simplified means for detecting and measuring changes `in capacitance between spaced stationary lelectrodes in .an oscillator. circuit. Y

A .specific Aembodiment of Athis invention-is lshown in the accompanying drawings in'which:

Figure l isfa diagrammatic illustration showing the circuit connections ofthe electrical components of the` improved 4.detecting means.

' Fig.. 2 isa top plan. view ofY a detectorchassis embodying the .improved .detecting means. p Fig. 3:.is a .fragmentary sectional View yofthe detecting electrodesof the device.of..FiS.-.2.-&S taken on line -3-3 thereof.

Fig. 4is a sectional elevationvasvtaken on :line 4-4 of Fig. 2,.indicating,v by ybroken lines, means for mechanically passing articles to be tested between the .detecting electrodes.

Fig.. 5 is a fragmentary perspective` view .show ing a shielded electrode.

Fig. 6 is a perspective view oia detector chassis arrangement for testing packaged. sheetmaterial such as currency.

, Fig. 7 Vis a front viewof thesame showing the termined or optimum capacitance in the capacitor; .and suitable means to utilize the current .changes in the oscillator grid circuit to actuate .electro-mechanical apparatus such as a meter or relay.

The particular circuit shown employs an oscillator .ofthe piezoelectric type wherein a suitable crystalin the oscillator gridcircuit is used to determine the basic frequency of the oscillator tank circuit, theobject being to provide an oscillatornin which-the amount of feedback is determined by the frequency and power factor of a tuned plate tank circuit incrder to obtain the sharpest or steepest frequency response to any variation, .from a tuned optimum, of the capacity of an air-gap capacitor. However, any suitable oscillator may oe used which is stable and sensitive to very smallchanges in capacity,V yet unstable enough through sensitivity to frequency changes to react favorably and cause a large changer-in feedback upon a small change in the .capacitance v-or power factor of the tank circuit.

-As shown, thegrid of the. oscillator tube is coupled-to the grid. of a suitable amplifier tube. Thus, when the plate or tank circuit of the oscillatoris tuned so that its frequency and power factor .are such that, `relative to the frequency and powerI factor of the oscillator grid circuit, proper phase and voltage relations are established .to 4sustain oscillation, .the oscillator grid will draw a negative current and thereby furnish bias tothe amplifier tube.

. Any .change vin the capacitance of the air-gap capacitor will produce a change in the oscillatory voltage and result in a changein the voscillator grid currentthereby changing the bias on the amplifying. tube so as tocause a change in the plate current of the .ampliflying tube.y This plate current of the amplifying tube may then be used vto .actuate a suitable indicating means or to operate a. relayicontrolling a separate operating circuit.

Preferably, .the-amplifying tube is of a type wherein a .small change 'in the grid voltage of the amplifying tube will produce a large change in theampliervplate current, sufcient to operate a-relay. or cause .a readilyreadable deflection of a meter. indicator.

Thus, the fundamental principle upon which .the improved-detector and measuring means opcrates ris .the measurement of the resultant capacitance or'powerfactor of a capacitor, produced by the dielectric characteristics of an article .under test, by the effect that such resultantcapacitance produces in detuning the plate tank circuit of the oscillator and thus varying the negative current of the oscillator grid, using such negative grid current change to control the operation of an indicating or amplifying device.

Referring particularly to Figure l of the drawings, the detecting means circuit, as shown, includes a vacuum tube oscillator I, such as a 6J5 tube, having a cathode 2, a plate 3, and a grid 4. The plate derives its energy by way o'v-a lead 5 from a conventional fB power supply,V represented in that portion of the diagram within f V the dot-dash outline A. The lead 5 is connected to the plate 3 through a variable'inductance 7,1

in parallel With which are a variable capacityL il,

and an air-gap capacitor 8. 'Ilfii's'pl'atel or' tank A circuit is by-passed to ground by. means of a con-.A

denser 9.

ftuning vthe oscillator plate or tank circuit by means of the variable capacitance El and inductance V`E so 'that the-amplitude of the oscillator 'tuloefgrid currentfis such as to cause the re- "quiredi'dilerehce'of potential to exist across the meter, 20.,or the relay 2I, or both, for their de- The grid 4 of the tube I is connected to ground at I0 through a 100,000 ohm resistor lI, and the L,

cathode 2 is connected to groundthrougha A470 ohm resistor I2 and a .0l mfd. by-pass condenser I3. A suitable crystal I4 is connected across the resistor I l toV ground, and a -lter'circuit comprising a 200,000 ohm resistor I5 and a .01 mfdfcondenser I6 are included to affordgreater stability. Also, as shown, the grid 4 of theoscillator is connected by a lead II to the grid I8 of a suitable amplifier I9. Y Y y The plate circuit of the amplifier I9 includes a suitable meter 20 and a sensitive relay- 2|, -arranged Vin parallel, and the amplier arrangement is such that the flow of current in the Aamplifier plate circuit will change rapidly and in inverse order upon any change in bias of the grid I8. Y l y In the oscillator grid circuit the current is negative with respect to the cathode, and thusthe ampliiier grid is biased negatively by the oscillator grid circuit voltage, and this regulatesI the flow of current in the amplier plate circuit. vThe amount of negative current or voltage in-the oscillator grid circuit is determined by-thecapacity of the capacitor 8,-and, once the oscillatorcircuit hasfb'eentuned, any variation of-the-capacity 8 will find immediate response through change in the negative grid potential, Whicli'in turn will arlect the ow-of current inthe amplier plate circuit. Thus, a decrease of the voltage-applied to-the grid I8 of the amplifier I0 will cause an increase in the ampliiier-platecurrent, or an increase of the grid voltage will cause a decrease of the amplifier plate current, andthe change Will at once be indicated on the meter 20 and cause actuation'of the relay 2l.

- The values of the inductance 'I yand capacitance 6 and the basic capacitance of the capacitor 8 are determined by the frequency at which the oscillator is to operate under standard or normal conditions and the physical and dielectric characteristics of the articles or objects to be tested. The physical characteristics of the articles or objects to be tested also determine the size and spacing of the electrodes or -plates comprising the Y capacitor 8. Y

Illustrative Values for the several -resistances and condensers that may be employed in the circuits of a typical detecting means are shown on the diagram of Figure 1, and in such a device the amplifier vIl may be a standard GSL? tube, fr:

and the meter 20 a sensitive 03O volt D. C. ldevice. The variable capacitance I54 may .be 050 mmfd., the variable inductance may be 15microhenrys, and in such case the capacitor 8 may sired operation.

'With 'respect to the relay 2I, it will be understood that the oscillator grid voltage value, and hence-'the "amplifier plate current, will be determined' byv whether itis desiredto lactuate the relay Auponl an increase of the capacitance of the capacitor 8, `or upon a decrease of such capacitance. Such amplifier-plate current will of course beindicated by the meter 2i).

If-=the device is to be operated merely as an indicating or-l counting means,- -the Value of the oscillator grid voltage-and thefresultant amplifier plate current' will preferablyv be such as to cause die meterfto'A indicate a value in the middle range of the meter scale, Whichindication becomes the base or optimum iromvfwhich variations are measured. This permits meter scale calibration to determine `increases aswell as decreases in-capacitance ybetween-the electrodesof the capacitor. Once -theoscillator tank circuit has been tuned tofa standard article'orobject, successive like articles or objects lmay be placed between the capacitor electrodes, and any variation of the dielectric characteristics-or capacitance of such articlesl from Vthe standard to .which the system is tuned-.will result in detuning the tank circuit and cause a change in the Voltage of the oscillatorgrid` due tofchange in oscillator frequency and feedback.- Such lchange of oscillator grid voltage produces a change of bias in the amplier tube, and results in a greater orlesser current flow in theamplier. lplate circuit, depending upon Whetherthe capacitance of the article tested is greater or lessthan that of the standard.

It .will be understoodv that the oscillator must become heatedbefore initial tuning to avoid frequent retuning due to frequency variation caused by temperature change, and that upon the oscillator reaching a normal operating temperature, initial tuning maybe done by means of a meter, not shown, in thegrid-cirCuit', or by means of the meter 20, the tuning beingfdone to a `standard spacing or air-gap between the electrodes of the capacitor 8'.y Also, if desired,` a temperature compensating device, vnot shown, may be installed across the oscillator plate circuit, which compensating device vvaries in capacity with temperature and serves to correct for the variations in capacity which ture-- A It'should als'obe understood that in some applications of the limproved detecting means, the Voltage' change in the oscillator grid circuit may be used directly to actuate a meter, thus obviating'the, need vfor the amplifier. `Such an application would be, forexample, counting the numoiccurlwith changes of temperacomprise copper or brass plates 15/3" x 3 spaced it?) ber of metal objects yina sealed Package, The

ainlialiiierl is employed whcregreater sensitivity of meter indications'A is required, as -inv the counting of paper Asheets ina package, determining'whether a predetermined number-f sheetsis contained in a package, or detecting the `presence of foreigner non-'standard sheets-in va package. fAlso, if the device is to -actuate areject mechanism, or'any other electromechanical means requiring the use of' a heavier relay than the relay 2l, the lrelayfZI may bel arranged toV -actuate 'a Asecon'd,'rheavierre lay `2 |.l as'shownin Fig. l.7

vThe improved-measuring and detecting means may be embodiedv innumerous arrangements of apparatus designed to suitably dispose the spaced yelectrodes -ofy the capacitor L8 so that' vthe objects to be tested may be successively introduced between the electrodes v4of the-capacitor, either manually or mechanically. Y

.One'form of such apparatus is shown in Figures Zand 4 Vci. the drawings'and comprises a chassis or housing 22 containing most ofthe electrical components of the detecting and measuring means, and arranged to support the air-gap capacitor electrodes on its upper side. As indicated in Figures 3 and '4,the upper 'end of the chassis 22 is .arranged to provide an open channel 23 extendingfrom side to side'of the chassis. The lowermcst electrode 24 of the detecting capacitor is disposed at the bottom of the channel 23, and is mounted in a suitable dielectric or insulating block 25 which insulates the electrode 24 from the chassis body. The uppermost electrode 26, also mounted in an insulating block 21, is carried on the underside of a plate 28 adjustably supported on four screw posts 29 by means of nuts 30, whereby the spacing or distance between the plates 24 and 26 may be adjusted or varied. Four supporting posts 29 are employed, since it is essential that the plates 24 and 26 be in parallel planes.

In cases where the article or object to be tested is non-conducting, the electrode plates 24 and 26 may be exposed, since in such case the contact between the article to be tested and the electrodes will not affect the operation of the detecting means. Where, however, the article or object to be tested has exposed conductive parts, it is necessary to wholly insulate the electrodes from the article or object, and this may be done by enclosing the electrode completely within a shell or covering of dielectric material as indicated in Figure 5.

As shown in Figure 5, an enclosed electrode such as the plate 3l will be completely surrounded by the dielectric material 32. It will be understood that the lead for connecting the electrode into the oscillator plate circuit will be attached to the electrode by suitable means, not shown, extending through the dielectric covering. The capacitative effect of this dielectric covering is compensated for by the initial tuning adjustment of the Oscillator circuit.

In the form shown in Figure 4, the apparatus is arranged to pass the article or object to be tested between the electrodes 24 and 26 from one side of the apparatus, and to deliver the tested articles from the opposite side. As will be understood by those skilled in the art, the articles to be tested may be automatically positioned between the electrodes by means of a suitable conveyer, indicated by the dot-dash line 33, and the tested articles may be delivered onto a second conveyer indicated by the broken line 34. In such an arrangement, the delivery conveyer y33 will deliver articles successively to the space between the electrodes 24 and 26, and suitable means, not shown,

6 willb provided-to control the cuplirigfbetwell -thenscillatorv and the amplifier automatically-so that VsuchV circuit will be interrupted except for thetimelthat an articleto be tested iscentered between the electrodes 24 andZG. `lhiswillavoid undue vibration of the meter indicatorand undesired actuation of the relay 2| during exchange of the test objects.

-As' shown inFigures 2 and 4, the oscillatortube I and the crystall I4 aremounted on the upper end of4 the chassis, the purpose being to keep the oscillatorftube las near the ldetector plates `or electrodes 'as possible, and to shorten the leads ofthe oscillator circuit as much as possible.

*Another lform of 'apparatus embodying the improved'detecting*means is shown in vFigures 6l and "7- of the drawing. This form of apparatus isv designed formanual` insertion of the article' to be-tested between the electrode plates,v and `is particularly adapted to counting sheets of paper in a package, or the number of bills inl a package of currency, the apparatus being providedwith a meterby means ofjwhich variations from a. predetermined standard may be visually determined.

As `shown in'Figures Gand '7, the'electronic 'detecting equipment is housed within a chassis "35, and the'detecting electrodes aredisposed vertically at the top'of the' chassis 35,'and arranged as the side walls of a slot or pocket in which the article to be tested is inserted. In this case, the detecting electrodes 36 and 3l are preferably entirely enclosed within a protective covering of a suitable dielectric material so that there will be no danger of an electrically conductive material coming into contact with the electrode plates. As shown, the meter 38 is disposed on the front face of the chassis 35 so as to be readily readable; and the tuning knobs 39 and 4i] for adjusting the variable capacitor 6 and the variable inductor 7, respectively, are also brought to the front side of the chassis 35 for convenience in tuning the oscillator circuit. In this device, red and green lights 4| and 42, respectively, are also provided, which lights are controlled through the oscillator grid circuit to indicate green when the oscillator is in tune, and red Whenever the oscillator is detuned.

The meter 38, in this form of apparatus, may be calibrated to suit the particular operations which are expected to be performed by the apparatus. For example, for checking packages of currency, the meter may be calibrated to indicate the actual count of the number of bills contained in the package.

The main advantages of this invention reside in the simplicity of the circuit and the electrical components thereof for detecting and determining small Variations, from a predetermined standard, of the capacity or dielectric character of the article or object being tested. Other advantages reside in the application of the negative voltage in the oscillator grid circuit for controlling the operation of a meter or a relay, or both, in response to changes of frequency in an oscillatory circuit occasioned by detuning of the oscillatory circuit due to change of capacitance, thereby providing extreme sensitivity in the detecting or measuring operation. Further advantages reside in the suitability of the device for use in counting, or determining the correctness of count, of objects contained in a closed or sealed package, such as packaged coins or tokens where the objects are not visible.

Still further advantages are to be found in the fact that the improved detecting and measuring means is more simple in construction, and more siy' operated than thebeat frequency oscillators and frequency modulation detector circuits heretofore used for similar purposes-and `permits the use of cheap, rugged, long life tubes that are ordinarily not suitable for sensitive measuring apparatus.l Y, lAlthough but one speciiic embodiment of this invention is hereby shown and described, it will be understood that details of construction and arrangement of the circuits and devicesrshown may be altered or omitted without departing from the spirit of this invention as defined by the vfollowing claims.

I claim:

1. A testing means of the class described com- ,prising a piezoelectric oscillator having an airgap capacitor in its tank circuit adapted to receive an article to be tested, means in said tank circuit .to tune said oscillator with the capacity of a predetermined standard, an amplifier tube having a control grid, means coupling the crystal circuit Aof said oscillator with the control grid of the amplifier to variably bias saidampliiier by means of the voltage changes in said crystal circuit, and means controlled by the output of said amplifier' to determine the eiTect upon the crystal circuit voltage due to variation of capacitance between said standard and the article being tested.

2.; A -testing means of the class described coiprising a vacuum` tube oscillator having an air- -gap capacitor. in its tank circuit and piezoelectric means in its grid circuit, said capacitor having a pair of spaced electrode plates arranged to receive an article; to be tested, means in said tank circuit to tune said oscillator with a predetermined standard capacitance in said capacitor, and means 4responsive to voltage change in the grid circuit of the oscillator tube arranged to indicate a change of capacity of said capacitor.

. v i MADELINE MAY.

' 'REFERENCES VCITED The following references are of record in the file of this patent:v

`UNITED STATES PA'I'ENTS Crawley May 7,1946 

